The present invention relates to ballast circuits for powering high intensity discharge (HID) lamps, and more particularly to a ballast circuit with an ignitor circuit for starting plural HID lamps connected in series.
An HID lamp, such as a metal halide, ceramic metal halide (CMH), high pressure sodium, or mercury lamp, is typically powered by an electromagnetic ballast circuit incorporating an iron core. The ballast transformer receives voltage from a power source, and outputs a ballast voltage for driving the lamp. The ballast circuit, which uses the iron core to achieve the necessary voltage adjustment, represents a major component of ballast cost, as well as bulk. The foregoing type of ballast circuit typically suffers the problem of powering only a single HID lamp.
U.S. Pat. No. 5,986,412 to Collins provides a ballast circuit for a plurality of serially connected, high-pressure gas discharge lamps. The ballast circuit comprises an electromagnetic ballast arrangement receptive of an input power signal, providing an output ballast voltage for driving the plurality of lamps, and providing an open circuit ballast voltage when the lamps are disconnected from the arrangement. A first ignitor circuit is connected between the ballast arrangement and the first lamp, and produces at least one ignitor pulse of high voltage and high frequency compared to the open circuit ballast voltage, to initiate starting of the first lamp. A second ignitor circuit is connected between the first lamp and a second lamp so as to be supplied with current through the first lamp. The second circuit produces at least one ignitor pulse of high voltage and high frequency compared to the open circuit ballast voltage after the first lamp begins to start and drops substantially in impedance, to initiate starting of the second lamp.
It is desirable to start a plurality (e.g. dual) of HID lamps with an ignitor circuit. If the ignitor circuit can start a plurality of HID lamps, it can eliminate redundant parts and reduces per-lamp ballast/ignitor cost.
The invention overcomes the foregoing problem in several exemplary embodiments that comprise a ballast/ignitor circuit capable of starting a plurality of HID lamps. In one aspect of the invention, a ballast/ignitor circuit is provided for serially connected HID lamps. In an embodiment of the invention, the ballast circuit comprises an electromagnetic ballast arrangement receptive of an input power signal, providing an output ballast voltage for driving the lamps; and an ignitor circuit connected to the ballast arrangement and to each lamp for starting all of the lamps and for producing at least one ignitor pulse to start each lamp.
In another embodiment of the invention, the ballast circuit comprises an electromagnetic ballast arrangement receptive of an input power signal, providing an output ballast voltage for driving the plurality of lamps, and providing an open circuit ballast voltage when the lamps are disconnected from the arrangement; and an ignitor circuit connected to the ballast arrangement and to each lamp for starting all of the lamps and for producing at least one ignitor pulse of high voltage and high frequency compared to the open circuit ballast voltage to start each lamp.
In another aspect of the invention, the ignitor circuit provides for starting each of serially connected, high intensity discharge lamps. In an embodiment of the invention, the ignitor circuit comprises a voltage-breakover device; a first capacitor with a first lead coupled to a first lead of the voltage-breakover device; a resistor with a first lead coupled to the first lead of the voltage-breakover device and first lead of the first capacitor; a pulse autotransformer associated with each subsequent serially connected, high intensity discharge lamp after a first lamp of serially connected lamps, each autotransformer having a winding connected between two serially connected lamps and a tap; and a second capacitor with first and second leads, wherein the first lead is coupled to a second lead of the resistor and the second lead is coupled to the tap of the pulse autotransformer.
In another embodiment of the invention, the ignitor circuit comprises a voltage-breakover device; a first capacitor; a resistor with a first lead coupled to a first lead of the first capacitor; a pulse transformer associated with each subsequent serially connected, high intensity discharge lamp after a first lamp of the plurality of serially connected lamps, each pulse transformer having a primary winding and a secondary winding, wherein the secondary winding is connected between two serially connected lamps and the primary winding is connected between the voltage-breakover device and the coupled first capacitor and resistor; and a second capacitor with a first lead coupled to a second lead of the resistor and a second lead coupled to a first lead of the secondary winding, said first lead of the secondary winding also being coupled to a preceding serially connected lamp.